The present invention relates to a device for perforating rod-shaped items.
In particular, the present invention relates to a perfected device of the aforementioned type, which may be used to particular advantage for the manufacture of cigarettes or similar, to which the following description refers purely by way of example.
In the cigarette manufacturing industry, so-called ventilated cigarettes are known to be produced featuring a number of holes in the filter for enabling a certain amount of air to be inhaled along with the smoke, and so rendering the same less harmful by reducing its strength and temperature.
Said ventilation holes are known to be formed using perforating devices comprising a coherent light (laser) source.
One such device is described in U.S. Pat. No. 4,647,752 filed by the present Applicant and the content of which is included herein purely by way of reference as required. This comprises a cigarette transfer roller designed to turn about its axis and having peripheral seats parallel to the same. The cigarettes are fed by a supply roller into said seats, which also turn about their respective axes at constant speed, and, at the end of a so-called perforating arc, are unloaded on to a pick-up roller. A laser beam generating unit directs a laser beam, coaxial with the transfer roller, on to a reflecting element consisting of a mirror turning faster than the transfer roller and driven by the same means. As the mirror turns, therefore, a reflected laser beam successively strikes a number of focusing lenses assigned to each seat, so as to form a perforation in each cigarette at each pass.
The number of perforations formed in each cigarette therefore equals the number of complete turns made by the reflecting mirror in the time taken for each cigarette to travel over said perforating arc. Said perforations are equally spaced about the circumference of each cigarette, or arranged in the form of a spiral, if said seats are turned repeatedly and moved axially at the same time.
Any change in the amount of ventilation provided for is made by varying the number of holes formed by the perforating device.
In the case of the aforementioned known device, this is achieved using devices for deflecting, intercepting or cutting off the laser beam, and so varying the number of perforations in relation to the number of turns of the reflecting mirror as each cigarette travels over said perforating arc.
Known regulating systems of the aforementioned type present a number of drawbacks. In addition to having to provide the perforating device with said laser beam deflecting, intercepting and cut-off means, these require a good deal of painstaking work on the part of the operator, thus resulting in production holdups and impaired flexibility. Also, due to operation of said systems consisting in intercepting or cutting off the laser beam in given perforating positions, the resulting perforations on the cigarettes are not equally spaced.